The invention relates to charge pump-type DC/DC converters.
Many electronic circuits require in addition to the supply voltage further voltages at a level sometimes above that of the supply voltage. One low-cost, simple and more particularly, as compared to coil-type converters, highly compact solution for providing these further voltages are charge pump-type voltage converters. Such converters are described e.g. in the text book xe2x80x9cThe Art of Electronicsxe2x80x9d by Paul Horowitz, 2nd Edition, Cambridge University Press, New York 1991 on pages 377 to 379 thereof.
Horowitz also describes a simple charge pump-type DC/DC converter with which an output voltage roughly corresponding to maximally twice the input voltage is achievable. The basic circuit of the converter consists substantially of a capacitor and four controllable switches (e.g. MOSFETs), one electrode of the capacitor being connectable via a first switch to the input voltage terminal of the converter and via a second switch to ground, and the other electrode of the capacitor being connectable via the third switch to the input voltage terminal and via the fourth switch to the output voltage terminal of the converter. The converter comprises in addition a control circuit including a clock signaling the switches so that in a first phase of the clock cycle, the so-called charging phase, the second switch and third switch are ON whilst the other switches are OFF so that the capacitor is charged to the input voltage, and in a second phase of a clock cycle, the so-called discharge phase, the first switch and the fourth switch are ON whilst the other switches are OFF so that now the charged capacitor is connected in series to the input voltage, resulting at the smoothing capacitor located at the output of the circuit in a voltage value roughly corresponding to twice the input voltage. In actual practice the converter is regulated by a regulator mechanism to a predefined fixed output voltage, depending on the concrete requirements of the application concerned, this output voltage being in the range between the input voltage and twice the input voltage.
Since charge pump-type DC/DC converters often need to be accommodated as an IC in small portables, e.g. mobile phones having a (rechargeable) battery power supply, it is good practice to produce for these applications the converters, firstly as small as possible, i.e. taking up minimum circuit area and secondly in minimizing the energy consumption of the converters to save the (rechargeable) battery.
Since the input voltages of the converter as furnished by the (rechargeable) battery very often fall off heavily during the lifetime of the (rechargeable) battery these converters must be able to provide a voltage gain which needs to be sufficient to furnish the portable with the necessary voltage even when the voltages supplied by the (rechargeable) battery is at a minimum useable. When the voltage range to be covered by the power supply is large, cascaded DC/DC converters are put to use preferably in which several elementary stages corresponding in configuration e.g. to the aforementioned charge pump and as described by Horowitz, each comprising a charge pump capacitor and several controllable switches connected in series, whereby the input of the kth stage is connected via one of the controllable switches of the kxe2x88x921th stage to the output of the kxe2x88x921th stage. Two stages thus already permit achieving a voltage gain of 4 and three stages a voltage gain of 8. In general the voltage gain of control circuit having N stages can be equated from the formula 2N.
Cascaded converters are known from prior art and described e.g. in U.S. Pat. No. 5,635,776.
One disadvantage of known cascaded DC/DC converters of the aforementioned kind is that the efficiency of the converters is relatively poor, the internal resistance relatively high and the converters permit attaining only a single voltage gain value.
An advantage of an embodiment of the invention is to provide a cascaded DC/DC converter which as compared to existing converters permits achieving a substantially higher efficiency and various voltage gain values.
A further aspect of the invention is to provide a cascaded DC/DC converter whose internal resistance is reduced as compared to that of existing converters.